Myelin deposition and maintenance is a critical component of nervous system function. Medical consequences of the inability to deposit and/or maintain this membrane, which range from minor motor and sensory deficits to severe mental retardation and early death, are directly related to the severity of myelin loss. Although much is known about the structure and the function of the myelin membrane, the mechanism of the highly ordered and selective elaboration of this membrane is not understood. In fact, in sharp contrast to the peripheral nervous system where myelination requires neuronal contact, a direct role for neurons in central nervous system (CNS) myelination has not been established. We believe that neurons do take pan directly in myelination and our goal is to identify axonal proteins that are involved. Our approach has been to generate monoclonal antibodies specific for axonal plasma membrane proteins and examine the ability of these antibodies to interfere with CNS myelinogenesis. For an in vitro myelination bioassay, we developed a system which utilizes rat cerebellar slice cultures to assess myelin production and deposition. Using this bioassay, we have identified an anti-axolemmal monoclonal antibody that inhibits myelination. Our preliminary characterization of this monoclonal indicates that it is directed against one or two neuronal cell surface proteins, likely to play a direct role in myelination in both the central and the peripheral nervous system. The primary objective of this research proposal is to isolate and characterize these proteins in order to determine their precise role in myelination. Purification, cloning and functional analysis will serve as a paradigm for examination of additional axolemmal proteins identified in further screens using the myelination bioassay. The approach which we describe here will allow the identification of these proteins and enable the elucidation of their function. Only after the key participants are known, will we be able to fully understand the mechanism of myelination.